1. Field of the Invention
The present invention relates to a multi-channel rotary joint that is mounted, for example, at the arm joint of an industrial robot used as a wafer conveyance means in a semiconductor manufacturing apparatus, where the rotary joint is used to allow a plurality of fluids of different pressure (such as a positive pressure fluid and a negative pressure fluid) to flow along separate routes between two relative rotational members that constitute an arm joint or the like.
2. Prior Art
In an industrial robot used as a wafer conveyance means in a semiconductor manufacturing apparatus, for example, a rotary joint is necessary for allowing a plurality of fluids of different pressure to flow between two relative rotational members that make up an arm joint (a working arm member and a power source arm member that rotatably supports the working arm member).
More specifically, the working arm member is provided with a plurality of rotary fluid passages connected to a vacuum chucking device for holding a workpiece (such as a silicon wafer), a fluid device for controlling the position of the working component, or the like, while the power source arm member is provided with a plurality of stationary fluid passages connected to a vacuum pump, a compressor, or another such power generation device for operating manipulation and control devices, and a rotary joint having a plurality of fluid routes is necessary for rotatably and independently linking these rotary fluid passages and stationary fluid passages.
One such rotary joint that has been proposed is designed such that the relative rotational portions of the channels formed between a joint housing and a rotator rotatably supported around the inner periphery of the joint housing are sealed with mechanical seals or elastic seal rings between the opposing peripheral surfaces of the joint housing and the rotator.
However, with a mechanical seal, a seal ring provided for the joint housing and a seal ring provided for the rotator are pressed into contact with each other by springs, creating a seal through the relative rotational sliding action of the two seal rings, and this construction took up a large installation space. Therefore, with a rotary joint that makes use of mechanical seals, if many channels are to be formed between the joint housing and the rotator, then the rotary joint must be made larger than necessary in order to leave enough space for the installation of the mechanical seals, and this hinders efforts to make the robot more compact.
Also, since the seal rings of the mechanical seals are powerfully pressed into contact with each other, if there are many channels (i.e., mechanical seals) installed, then there is high rotational resistance between the joint housing and the rotator, the load and resistance with respect to the movement of the robot arm increases, and there may be an adverse effect on the robot performance.
In contrast, the above problems are not encountered with a rotary joint that makes use of elastic seal rings such as O-rings as its sealing means. However, in this rotary joint, the sealing force is obtained via the elastic contact force of the seal rings that applies against the opposing peripheral surfaces of the joint housing and the rotator. Accordingly, stable sealing cannot be obtained for high-pressure fluids or negative pressure fluids, and such a rotary joint cannot comply adequately with fluctuations in fluid pressure.
Accordingly, it is an object of the present invention to provide a multi-channel rotary joint in which the advantages to use elastic seal rings (such as compact sizing of the joint) is maintained without any drawbacks (for instance, a poor sealing performance).
It is another object of the present invention to provide a multi-channel rotary joint that allows a plurality of fluids of different pressure (such as fluids of positive and negative pressure) to flow under control as desired in separated routes between relative rotational members without mixing the fluids.
It is still another object of the present invention to provide a practical multi-channel rotary joint that is used, to advantage, in arm joints and so forth of industrial robots such as a wafer conveyance robot.
The above objects are accomplished by a unique structure for a multi-channel rotary joint that comprises:
a joint housing;
a rotator rotatably installed in the joint housing;
a plurality of elastic seal rings disposed in a row in an axial direction of the rotator so as to be between opposing peripheral surfaces of the joint housing and the rotator, wherein each of the elastic seal rings is comprised of an annular main body and cylindrical inner and outer peripheral lips that protrude axially from the annular main body and are brought into an elastically pressing contact with the opposing peripheral surfaces;
a low-pressure channel space and a high-pressure channel space formed between the opposing peripheral surfaces and sealed by two opposing elastic seal rings, wherein two elastic seal rings that seal the low-pressure channel space being engaged with and supported by one of the opposing peripheral surfaces such that annular grooves between inner and outer peripheral lips of the elastic seal rings are disposed symmetrically and open into spaces adjacent to the low-pressure channel space, and two elastic seal rings that seal the high-pressure channel space being engaged with and supported by one of the opposing peripheral surfaces such that annular grooves between inner and outer peripheral lips of the elastic seal rings are disposed symmetrically and open into the high-pressure channel space; and
a low-pressure channel and a high-pressure channel provided between the joint housing and the rotator, wherein a fluid lower in pressure than a space adjacent to the low-pressure channel space is allowed to flow into the low-pressure channel that communicates with the low-pressure channel space, and a fluid higher in pressure than a space adjacent to the high-pressure channel space is allowed to flow into the high-pressure channel that communicates with through the high-pressure channel space.
With the above structure, the low-pressure channel is used as a vacuum suction route through which a negative pressure fluid flows, and the high-pressure channel is used as a pressurized fluid supply route through which a positive pressure fluid flows. At least one low-pressure channel space can be provided adjacent to a high-pressure channel space; and in this case, the elastic seal ring that seals the low-pressure channel space can be used also as an elastic seal ring that seals the high-pressure channel space. Also, an electrical wire passage hole can be formed along the axial line of the rotator so as to penetrate through the joint housing and the rotator. It is preferable to install a rotary connector that connects electrical wiring at the end of the electrical wire passage hole.